Clinical Etiological Survey of a Population of 471 Mentally Retarded Patients Living in an Institution in the Southern Part of the Netherlands

Abstract

Objective: Investigation of etiological factors in mental retardation (MR). Methods: On 471 adults (mean age 46 years; 92.6% males) living in an institution for the mentally retarded, clinical examination, cytogenetic and molecular studies and basic metabolic screening were performed. Results: Chromosomal abnormalities were found in 100 patients (21.2%). Of these, 87 had numerical autosomal abnormalities (all Down syndrome), 7 structural autosomal abnormalities and 6 numerical abnormalities of sex chromosomes. Monogenic disorders were diagnosed in 61 patients (13%): 14 autosomal dominant, 25 autosomal recessive and 22 X-linked conditions. In 1.7% (n = 8) of the patients a central nervous system (CNS) malformation was documented. Acquired CNS disorders were diagnosed in 69 patients (14.6%): a prenatal cause was found in 15 patients, a perinatal in 27 and a postnatal cause in 27. In 233 patients (49.5% of the total sample; 215 males and 18 females) idiopathic MR was present. In this group there were 2 patients with a high degree of consanguinity (incest). In one third (n = 73; 31.3%) of these patients there was a family history of MR (MR in first and second-degree relatives). Pedigree data were most compatible with X-linked MR in 35 males from 32 different families, i.e. 47.9% of the patients with idiopathic MR and family history of MR, and 15% of the total group of patients with idiopathic MR. Thus, X-linked inheritance was considered in a total group of 57 males, accounting for 12.1% of the total population: known X-linked disorders in 22 males and non-specific X-linked MR in 35 males. Minor anomalies were present in 41 patients (17.6%). Their presence was significantly associated with the severity of the MR. Neurological abnormalities were present in 47 patients (20.2%), with CNS dysfunction (central paresis, dyskinesia, ataxia) in 45 (19.3%). Seizures were present in one third of the patients (n = 78) and a statistically significant correlation between the level of MR and the presence of seizures was found. In the group of males with idiopathic MR, the number of males with the combination of microcephaly and micro-orchidism was higher than expected, but not statistically significant and the number of males with the combination of macrocephaly and macro-orchidism was statistically significantly increased (n = 5; 2.3%). Before systematic evaluation, only 21.8% (103/471) of the patients had a known diagnosis. After this survey, 50.5% (238/471) of the investigated patients had a definite diagnosis. Conclusion: Establishing the diagnosis in older mentally retarded patients is important in the prevention of medical complications and in the development of management strategies for the institution. Finally, it is the conditio sine qua non for genetic counseling of the respective families.